A Comparison of Ferrite Growth Kinetics under Denitriding and Decarburizing Conditions
- PDF / 839,977 Bytes
- 6 Pages / 593.972 x 792 pts Page_size
- 88 Downloads / 141 Views
UCTION
THE precipitation of ferrite from austenite during cooling is a critical step in the production of many grades of steels. There have been many attempts to model the kinetics of this phase transformation.[1–3] The complexity of the problem is mainly due to the large difference between the diffusivity of the substitutional solutes such as Mn and Si and that of interstitial elements such as C and N. A direct consequence is that ferrite growth can MINGXING GUO, formerly Post-Doctoral Fellow at the Department of Materials Science and Engineering, McMaster University, Hamilton, ON, now is Associate Professor with the State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing, P.R. China. DAMON PANAHI, formerly Post-Doctoral Fellow at the Department of Materials Science and Engineering, McMaster University, now is Research Engineer with the ArcelorMittal, East Chicago, IN. HUGO P. VAN LANDEGHEM, formerly Post-Doctoral Fellow at the Department of Materials Science and Engineering, McMaster University, is now Post-Doctoral Fellow with the Institut Jean Lamour, Universite´ de Lorraine, Nancy, France. CHRISTOPHER R. HUTCHINSON, Associate Professor, is with the Department of Materials Engineering, Monash University, Clayton, 3800 VIC, Australia. GARY R. PURDY, Professor, and HATEM S. ZUROB, AssociateProfessor, are with the Department of Materials Science and Engineering, McMaster University, Hamilton, ON, Canada. Contact e-mail: [email protected] Manuscript submitted November 3, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
proceed with or without the partitioning of the substitutional alloying element. The first scenario is observed at low supersaturations, while the latter is observed when the supersaturation is high. The non-partitioning mode of ferrite growth is the more technologically relevant growth regime, and two limiting models have been proposed to describe the growth kinetics. A presumed upper limit is offered by the ParaEquilibrium (PE) model[4,5] which assumes that the substitutional elements are immobile (even as the interface migrates) leading to the same ratio of substitutional solute atoms to solvent atoms in the parent and daughter phases. An alternative is the local equilibrium negligible partitioning model (LENP),[5–7] where a local equilibrium tie line is selected such that long range diffusion of the substitutional elements is not required to take place. This usually requires the (theoretical) existence of an alloying element spike (positive or negative) at the migrating interface. Examples of the limits for ferrite growth under the PE and LENP models are superimposed on an isopleth of the Fe-2Mn-C (wt pct) system shown in Figure 1.[8] Although the PE and LENP models are thought to represent limits of behavior, one might expect the PE model to be increasingly relevant at lower temperatures (where atomic mobility is limited) and the LENP model to be more relevant at higher temperatures. The implication is that the growth mode may indeed change
Fig
Data Loading...
